How does Tame Beast work?

For the life of me I cannot get it to tame anything. Any help is appreciated!

First of all it need to be a Beast type mob

use the skill when on low life a purple/pink icon should appear under their life bar

Kill it

It takes the gem and converts it into a "minion" gem

*WARNING* you will loose that Tame beast Gem

Man I feel dumb. I've been struggling trying to "capture" mobs not realizing it HAS to be beast. Glad to know.

You can disenchant the beast to get a tame beast gem back